During well-drilling operations, formations are often encountered which lose physical and dimensional integrity when exposed to aqueous drilling fluids (muds). In most cases, such formations comprise reactive shales. Prior to the advent of oil-based, emulsion and invert emulsion muds, great difficulty was encountered in drilling these types of shales. On the other hand, while hydrocarbon-containing muds make drilling through reactive shales possible, they pose safety and environmental hazards and can interfere with well-logging operations.
A variety of water-based drilling additives has been developed over the years in an attempt to deal with shale drilling problems effectively while avoiding the problems encountered when oil-based muds were used.
Sawsdon, in U.K. Patent Application 2,089,397A, disclosed an aqueous wellbore fluid for use in drilling, well completion, packing, perforating or workover fluid containing at least 20% by weight of potassium carbonate; optionally a water-soluble polymeric viscosifier, such as carboxymethylcellulose, was added to the wellbore fluid. Gray et al., in “Composition and Properties of Oil Well Drilling Fluid”, 4th Edition (Gulf Publishing Company 1980), reported the use of potassium salts in drilling fluids to suppress the swelling of bentonite, potassium chloride being preferred. Another standard industry reference that describe the shale stabilizing effect of the potassium ion in polymer muds may be found in SPE 10100 “Fundamentals and Use of Potassium/Polymer Drilling Fluids to Minimize Drilling and Completion Problems Associated with Hydratable Clays,” by R. P. Steiger, presented at the 56th Annual Fall Technical Conference, Dallas, Tex., Oct. 5–7, 1981. U.S. Pat. No. 4,447,341, to Block relates to a drilling fluid containing A10(OH) and a crosslinked polyvinyl alcohol together with a potassium salt, such as potassium chloride, as a clay-stabilizing composition. Coffey et al., in the Oil & Gas Journal, Jan. 27, 1987, described shale inhibition using an aqueous system, maintained at a pH of 9.0 or less, which contains an unidentified nonionic polymer combined with potassium phosphate complex of undefined composition. Peterson in U.S. Pat. No. 4,780,220 discloses the use of glycerin, polyglycerin, and mixtures thereof in a drilling mud to inhibit the swelling of clays.
The technology of choice for aqueous-based shale-stabilizing muds involves the use of partially hydrolyzed polyacrylamide (PHPA) combined with potassium chloride. Scheuerman disclosed such a combination in U.S. Pat. No. 3,738,437 as part of a regimen for dealing with shale-drilling problems. Systems involving PHPA in combination with various electrolytes, including potassium chloride, at pH of 8.5 to 10.0, were also reviewed by Clark et al. in SPE/IADC 10681, presented at the Mar. 15–18, 1987 SPE/IADC Drilling Conference in New Orleans, La.
Cannon U.S. Pat. Nos. 2,109,858 and 2,191,312 generally disclose the addition of various polyhydroxy compounds, which includes certain carbohydrates such as sucrose, and an alkaline material, such as caustic soda, in aqueous drilling fluids for purposes of inhibiting shale swelling.
Salathiel U.S. Pat. No. 2,785,125 discloses a water base drilling fluid containing 1–15 ppb starch and 0.5–10 ppb of a water soluble heat degradation product of a saccharide containing 1 to 4 sugar units. The starch and degradation product combine to reduce the fluid loss of the drilling fluid. Salathiel U.S. Pat. No. 2,786,027 discloses a water base drilling fluid containing 1–15 ppb starch and 0.5–5 ppb of an additive having an average molecular weight of about 90 to 3000 and a ratio of carbon to oxygen of 1.5 to 2.7. The starch and additive combine to reduce the fluid loss of the drilling fluid. Walker U.S. Pat. No. 3,849,317 discloses a water base drilling fluid having a liquid phase saturated with calcium hydroxide containing as an additive for reducing gel strength and yield point, from ⅛ to 8 ppb of hydrolyzed cereal solids which is comprised of from about 15% to about 25% di-saccharides, tri-saccharides, tetrasaccharides, and penta-saccharides, and from 75% to 85% hexa-saccharides and above. Perricone et al. U.S. Pat. No. 4,941,981 discloses a drilling fluid for shale inhibition comprising a liquid phase containing: (a) a water phase comprising fresh water, sea water, brine, simulated brine, or mixtures thereof; and (b) a water-soluble component selected from the class consisting of polyhydric alcohols, glycol, glycol ethers, polypropylene glycols, polyethylene glycols, ethylene oxide-propylene oxide copolymers (“EO-PO”), alcohol-initiated EO-PO copolymers and/or mixtures thereof, the concentration of said water-soluble component in the total liquid phase being from about 5% to about 50% by volume.
Sheu et al. U.S. Pat. No. 5,110,484 discloses aqueous drilling fluids containing the browning reaction product of a carbohydrate, such as pentose, hexose such as fructose and glucose, as well as di- and poly saccharides, such as sucrose, lactose, mannose, cellulose, starch, dextrin, dextran, carboxymethylcellulose, rice and derivatives of such carbohydrates.
Drilling fluids containing alkali metal silicates have also been proposed for drilling shale-containing formations. Thus Vail et al., in U.S. Pat. No. 2,133,759, disclose muds containing alkali metal silicates. In U.S. Pat. No. 2,146,693, Vietti et al. disclosed a drilling fluid containing one of several sodium salts, including sodium silicate, the sodium salt content of the mud being in excess of 20% by weight. The following U.S. patents also disclose sodium silicate-containing drilling fluids: Vietti et al. U.S. Pat. No. 2,165,824; Garrison U.S. Pat. No. 2,239,647; and Garrison et al. U.S. Pat. No. 2,353,230.
Wingrave et al. U.S. Pat. No. 4,98,450 discloses drilling fluids containing a shale stabilizing additive comprising one or more water-soluble polymers which are capable of forming nucleophilic sites when treated with a base, such as partially hydrolyzed polyvinyl acetate, and one or more alkaline potassium salts in a weight ratio generally in the range between 1:20 to about 3:1, preferably from about 1:2 to about 1.5:1. Usually the additive is added to the drilling fluid at a level between 0.01 weight percent and 10.0 weight percent of the aqueous phase, typically between about 0.1 and about 4.0 weight percent, and preferably between about 0.3 and about 2.0 weight percent. The potassium salts are relatively strong Bronated-Lowry bases, such as potassium silicate, potassium carbonate, and tribasic potassium phosphate.
Mullen et al. U.S. Pat. No. 6,248,698 discloses silicate drilling fluids containing hematite weighing agents and manganese oxide bridging agents.
Although drilling fluids containing sodium and potassium silicates have been used for decades to combat shale problems, these fluids have had limited success for the following reasons: free soluble silicate in the drilling fluid reacts with accumulated drilled solids to create problems in control of the drilling fluid properties; free soluble silicate in the drilling fluid filtrate polymerizes or precipitates after invading a potentially productive formation to cause severe reduction in permeability; free soluble silicate in the drilling fluid precludes the use of lubricants commonly used for torque reduction.